Hydrophobicity Behaviour and Fibers Distribution of Two Different Woody Biomasses Torrefied at Different Conditions

This study investigates both the hydrophobicity behaviour of two types of biomasses and the evolution of their fibres content when thermally treated at different torrefaction degrees. The two woody biomasses have been chosen from softwood as spruce (picea abies) and annual grass lignocellulosic hardwood as reeds. Selected samples of the indicated biomasses were torrefied at different reaction time and temperature values, ranging from 250°C to 310°C, on a small batch reactor utilizing a direct flux of nitrogen as thermal carrier. Before treatment all samples were dried in a convection oven at 103 C° for 24 h. The Mass Yield Ratio (MYR) is the parameter utilized to define the torrefaction degree and, for this investigation, torrefied samples present a MYR of 90%, 80% and 70% for spruce and 80%, 70% and 60% for reeds. The hydrophobicity was determined in terms of EMC (Equilibrium Moisture Content) at a constant temperature of 25°C and Relative Humidity (RH) ranging from 24% to 75%. The fibres content, lignin, cellulose and hemicellulose, was determined for both raw and torrefied samples according to the so called Van Soest method. Regarding the hydrophobic behaviour, for both the biomasses, it can be observed that up to a MYR at 80%, the moisture absorption reduces progressively from raw to torrefied samples. Regarding the fibres content analysis, it is confirmed that as torrefaction becomes stronger in terms of MYR, a near-complete breakdown of hemicellulose is observed.